1. Field of the Invention
The present invention generally relates to heat exchangers, such as those of the type used in air-conditioning systems. More particularly, this invention relates to a heat exchanger tube configuration that incorporates integral fins for transferring heat to and from the tube.
2. Description of the Related Art
Heat exchangers are employed within the automotive industry as condensers and evaporators for use in air conditioning systems, radiators for cooling engine coolant, heater cores for internal climate control, etc. One type of heat exchanger construction used in the automotive industry for condensers and evaporators comprises a number of parallel tubes that are joined to and between a pair of manifolds, creating a parallel flow arrangement. The ends of the tubes are typically metallurgically joined (brazed, soldered or welded) to tube ports, generally in the form of holes or slots formed in a wall of each manifold. In order to maximize the amount of surface area available for transferring heat between the environment and a fluid flowing through the heat exchanger, automotive heat exchangers often have a tube-and-fin construction in which numerous tubes thermally communicate with high surface area fins. The fins are typically in the form of flat panels having apertures through which tubes with circular cross-sections are inserted, or in the form of sinusoidal centers that are positioned between adjacent pairs of “flat” tubes with oblong cross-sections. In either case, the resulting tube-and-fin assembly is oriented so that the edges of the fins face the fluid (e.g., air) flowing between the tubes, i.e., the fins are normal to the plane defined by the tubes of the heat exchanger.
Alternative forms of fins have been suggested, examples of which include U.S. Pat. No. 4,546,819 to O'Connor, U.S. Pat. No. 4,951,742 to Keyes, and U.S. Pat. No. 5,353,868 to Abbott. Each of these patents discloses a cooling tube whose outer surface undergoes a second forming operation to have integral fins. Abbott discloses fin strips formed by lancing a conduit, while O'Connor and Keyes disclose integral fins formed by rolling the exterior of a tube. An approach to forming integral fins on round plastic tubing is taught in U.S. Pat. No. 4,926,933 to Gray, in which integral helical fins are defined on the exterior of a round plastic tube during injection molding or extrusion of the tube.